1. Field of the Invention
The present invention relates generally to a power tool and in particular to an impact power tool having various speeds.
2. The Prior Arts
A conventional power tool used for drilling, screw driving, etc transmits power from a motor to an output shaft via gear systems at various speeds. Moreover, some power tools provide impact function to easily tighten or loosen screws.
Referring to FIG. 4, a conventional impact power tool comprises a motor 1, a first planetary gear set 2, a second planetary gear set 3, a clutch 31, a connecting bar R, an intermediate shaft 5, an output shaft 6 and a hammer seat 8. A drive gear shaft 11 mounted on the motor 1 engages with first planet gears 23 of the first planetary gear set 2. The first planet gears 23 are pivotally connected to a first planet carrier 25 with planet gear shafts 251. A plurality of clutch shafts 252 connects the first planet carrier 25 with the clutch 31. A rim of the clutch 31 is provided with a circumferential groove 312 to engage with a switch (not shown in the Figure) so that the clutch 31 moves with the switch. The clutch 31 is provided with a first sun gear G1 and a second sun gear G2. The first sun gear G1 is connected with the clutch 31 and engages with second planet gears 34 of the second planetary gear set 3. The second planet gears 34 are pivotally connected to a second planet carrier 35. The second planet carrier 35 comprises an internal gear 352 capable of engaging with the second sun gear G2. The first sun gear G1 and the second sun gear G2 are mounted on a sun gear shaft. One end of the intermediate shaft 5 is by the sun gear shaft, and is connected with the second planet carrier 35. The other end of the intermediate shaft 5 includes a polygonal hole 5A. A connecting bar R passes through central holes of the sun gear shaft and the intermediate shaft 5. One end of the connecting bar is connected with the clutch 31, and the other end of the connecting bar R comprises a polygonal block R1. The hammer seat 8, which comprises hammer blocks 81, sleeves on and is driven to rotate by the intermediate shaft 5. One end of the output shaft 6 comprises a polygonal hole 66 corresponding to the polygonal block R1 of the connecting bar R. The output shaft 6 further comprises projections 62 to be struck by the hammer blocks 81.
Referring to FIG. 4, when the clutch 31 moves axially to a first position, the first sun gear 61 engages with the second planet gears 34. Meanwhile, one end of the polygonal block R1 is in the polygonal hole 5A, and the other end of the polygonal block R1 penetrates and engages with the polygonal hole 66 of the output shaft 6. Therefore, the motor 1 drives the drive gear shaft 11 to rotate the first planetary gear set 2, the clutch shaft 252 drives the clutch 31 and the first sun gear 61 to rotate, the first sun gear G1 drives the second planetary gears 34 to rotate, and then the second planet carrier 35 drives the intermediate shaft 5 and the output shaft 6 to rotate at a low speed.
Referring to FIG. 5, when the clutch 31 moves axially to a second position, the first sun gear G1 disengages from the second planet gears 34, and the second sun gear G2 engages with the internal gear 352 of the second planet carrier 35. Meanwhile, the polygonal block R1 disengages and is away from the polygonal hole 66 of the output shaft 6. Therefore, the motor 1 drives the drive gear shaft 11 to rotate the first planetary gear set 2, the clutch shaft 252 drives the clutch 31 and the second sun gear G2 to rotate, the second sun gear G2 drives the second planet carrier 35 to rotate, and then the second planet carrier 35 drives the intermediate shaft 5 and the hammer seat 8 to rotate at a high speed. The hammer blocks 81 of the hammer seat 8 will strike and drive the projections 62 of the output shaft 6 to rotate, thereby providing rotation and impact at the same time.